U.S. patent number 4,698,017 [Application Number 06/940,142] was granted by the patent office on 1987-10-06 for orthodontic brackets.
Invention is credited to Gustaf H. Hanson.
United States Patent |
4,698,017 |
Hanson |
October 6, 1987 |
Orthodontic brackets
Abstract
The invention provides a new orthodontic bracket consisting of a
bracket body having a mesio-distal extending arch wire receiving
slot that opens to the labial surface. A latch member of "comma"
transverse cross-section is accommodated in a recess in the body,
being pivoted thereto by two spaced pivot pins passing through the
latch member body portion, while the latch member tail portion
moves between a closed position in which it closes the arch wire
slot to retain an arch wire therein, and an open position in which
the arch wire can be inserted in and removed from the slot. A load
spring for applying corrective forces to the arch wire is
accommodated within the body to the lingual side of the slot and is
a thin bowed sheet spring convex toward the latch so that it urges
the arch wire toward the latch lingual surface, the gingival part
of which is inclined lingually for cooperation with the arch wire
in controlling the movements of the bracket on the arch wire. The
latch preferably comprises a latch spring also accommodated within
the body, and also a thin bowed sheet spring convex toward the
latch member and engagable in the latch closed position with a
mesio-distal detent ledge on the latch body; the latch spring is
accessed for release of the latch by inserting a probe tool through
a bore passing through the latch member.
Inventors: |
Hanson; Gustaf H. (Hamilton,
Ontario, CA) |
Family
ID: |
25474309 |
Appl.
No.: |
06/940,142 |
Filed: |
December 10, 1986 |
Current U.S.
Class: |
433/11;
433/13 |
Current CPC
Class: |
A61C
7/285 (20130101); A61C 7/145 (20130101) |
Current International
Class: |
A61C
7/00 (20060101); A61C 7/28 (20060101); A61C
007/00 () |
Field of
Search: |
;433/8,10,11,21 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
American Journal of Orthodontics, Mar. 1961, vol. 47, No. 3 Spring
Rotation Bracket..
|
Primary Examiner: Peshock; Robert
Attorney, Agent or Firm: Rogers & Scott
Claims
I claim:
1. An orthodontic bracket comprising:
a bracket body having lingual, labial, gingival, occlusal, distal
and mesial surface portions and a mesio-distal extending arch wire
receiving slot in the labial surface portion;
a latch member pivoted to the body about a mesio-distal extending
pivot axis for movement between a closed position in which it
extends in front of the labial mouth of the slot to retain an arch
wire therein, and an open position in which an arch wire can be
inserted in and withdrawn from the slot by labial or lingual
movement thereof respectively;
a load spring disposed within the slot adjacent the lingual face
thereof for engagement by an arch wire inserted in the slot to urge
the arch wire labially against the latch member; and
latch means operative between the bracket body and the latch member
for latching the latch member in the said closed position.
2. An orthodontic bracket as claimed in claim 1, wherein the load
spring is a thin curved sheet spring member having parallel convex
and concave surfaces and disposed against a lingual face of the
slot with its convex surface facing the lingual face of the latch
member, the load spring being additionally stressed by engagement
with the arch wire that flattens it toward the said slot lingual
face.
3. An orthodontic bracket as claimed in claim 2, wherein the
gingival edge portion of the spring member is contained in a slot
extending gingivally from the gingival surface of the arch wire
slot and opening to the slot gingival surface to retain the member
in the arch wire slot for required engagement with the arch
wire.
4. An orthodontic bracket as claimed in claim 1, wherein the latch
means comprises a mesio-distal extending detent ledge on the latch
member, and a latch spring interposed between the bracket body and
the latch member to engage the detent ledge and hold the latch
member latched in the said closed position.
5. An orthodontic bracket as claimed in claim 4, wherein the latch
spring is a thin curved sheet spring member having parallel convex
and concave surfaces and disposed against a lingual face of the
bracket body with its convex face facing the latch member, the
latch spring being moved toward the bracket body lingual face to
disengage it from the latch member detent ledge and to release the
latch member to move to the said open position.
6. An orthodontic bracket as claimed in claim 5, wherein the latch
member has therein a bore through which the latch spring is engaged
by a tool to disengage it from the latch member detent edge.
7. An orthodontic bracket as claimed in claim 6, wherein the latch
member is pivoted to the bracket body by two transversely spaced
coaxial pivot pins, and the said bore passes between the facing
ends of the pivot pins.
8. An orthodontic bracket as claimed in claim 1, wherein the latch
member is of "comma" cross-section in the occlusal gingival plane
having a body portion and tail portion, pivot means pivoting the
member to the bracket body passing into the body portion, and the
tail portion closing the arch wire slot when the latch member is in
the closed position.
9. An orthodontic bracket as claimed in claim 8, wherein with the
latch member in the closed position the lingual face of the latch
member tail portion has the occlusal part thereof at least
approximately parallel to the slot lingual face, and the gingival
part thereof extending at an angle to the occlusal part toward the
slot lingual face.
10. An orthodontic bracket as claimed in claim 9, wherein the
gingival part of the lingual face of the latch member tail portion
extends at about 45.degree. to the occlusal part of the same
face.
11. An orthodontic bracket as claimed in claim 1, wherein the
portions of the lingual face of the arch wire slot on both sides of
the latch member are formed on a radius to be convex toward the
labial to conform with the curvature of an arch wire in the
slot.
12. An orthodontic bracket as claimed in claim 1, wherein the
lingual face of the bracket body is provided with two sets of
grooves for reception of cement for attaching the bracket to a
tooth, the grooves of each set being parallel to one another, the
grooves of one set being transverse to the grooves of the other set
to form residual pillars between them.
Description
FIELD OF THE INVENTION
The present invention relates to new orthodontic brackets employed
in procedures for applying corrective moving forces to teeth. The
invention is concerned especially, but not exclusively, to such
brackets intended for attachment directly to the tooth surfaces
employing a suitable cement system.
REVIEW OF THE PRIOR ART
There have been a number of different proposals for orthodontic
brackets that are fastened to the teeth and receive a connecting
light springy arch wire without the use of ligating tie-wires to
secure the arch wire to the brackets, and reference is made
specifically to those disclosed in my prior U.S. Pat. Nos.
3,772,787, 4,248,588 and 4,492,573, issued respectively Nov. 20,
1973, Feb. 3, 1981 and Jan. 8, 1985, which constitute the Hanson
"SPEED" system brackets now in use by many orthodontists. Such
brackets employ a retainer member of thin sheet spring steel
movable on a mesially-distally slotted body between open and closed
positions in which respectively the labially-opening slot in the
body is open to receive the arch wire, and closed to retain the
arch wire, the springy retainer member engaging the arch wire to
apply its spring force to the bracket and thereby to the tooth.
There is a constant endeavour in this field to provide brackets
that are as small and as smooth exteriorly as possible, both for
cosmetic reasons, and also to reduce as much as possible rough
contact of the brackets with the tongue and adjacent tissue of the
patient's mouth, which can otherwise cause discomfort. There is
also increasing interest in the so-called lingual technique in
which the brackets are mounted on the lingual tooth surfaces, so
that they are almost completely concealed, especially with adult
patients who are particularly concerned with appearance during the
two-three year period required for the average procedure. Small,
smooth brackets are particularly needed for this location because
of ready access by the tongue, and the natural tendency to explore
any foreign object in the mouth with the tongue. However, if
attempts are made to directly reduce the size of the existing
brackets they become subject to the well known phenomenon that
changes in scale do not affect all properties in the same ratio,
e.g. areas decrease in square ratio and volumes decrease in cube
ratio, with the result that it becomes difficult or impossible,
especially with the spring members, to find materials of the
required properties to maintain the necessary function.
DEFINITION OF THE INVENTION
It is therefore an object of the invention to provide a new
orthodontic bracket of the tie-less, arch wire receiving type that
is particularly suited for production in relatively small
sizes.
It is another object to provide such a bracket in which spring
members that are employed are concealed within the bracket and
protected against over stressing.
According to the present invention there is provided an orthodontic
bracket comprising:
a bracket body having lingual, labial, gingival, occlusal, distal
and mesial surface portions and a mesio-distal extending arch wire
receiving slot in the labial surface portion;
a latch member pivoted to the body about a mesio-distal extending
pivot axis for movement between a closed position in which it
extends in front of the labial mouth of the slot to retain an arch
wire therein, and an open position in which an arch wire can be
inserted in and withdrawn from the slot by labial or lingual
movement thereof respectively;
a load spring disposed within the slot adjacent the lingual face
thereof for engagement by an arch wire inserted in the slot to urge
the arch wire labially against the latch member; and
latch means operative between the bracket body and the latch member
for latching the latch member in the said closed position.
DESCRIPTION OF THE DRAWINGS
Particular preferred embodiments of the invention will now be
described, by way of example, with reference to the accompanying
diagrammatic drawings, wherein:
FIG. 1 is a front (labial) elevation of a complete bracket with the
arch wire retaining latch member thereof in the closed
position;
FIG. 2 is a cross-section (mesial view) taken generally on the line
2--2 of FIG. 1, but medially through the latch and load springs,
and showing also a tool employed for unlatching the latch
member;
FIG. 3 is a mesial view cross-section as FIG. 2, but with the latch
member in the open position;
FIG. 4 is a front elevation of the bracket body corresponding to
FIG. 1, but with the latch member removed for the latch and load
springs to be seen;
FIG. 5 is a top (occlusal) elevation of the bracket body, also with
the latch member removed;
FIG. 6 is a side elevation showing a central incisor tooth and a
bracket of the invention cemented to the lingual surface thereof,
as in the so-called lingual technique;
FIGS. 7(a) through 7(f) show different cross-sections of arch wire
suitable for use with the brackets of the invention;
FIGS. 8(a) and 8(b) are respectively front and side elevations of a
bracket with a round arch wire mounted therein and in a neutral
position;
FIGS. 9(a) and 9(b) are respectively views similar to FIGS. 8(a)
and 8(b) and showing the result of tilting the bracket relative to
the wire;
FIGS. 10(a) through 10(c) show, by way of example, the way in which
the arch wire of cross-section shown in Figure 7(f) cooperates with
the bracket to produce tilting of the tooth to which it is
attached;
FIG. 11 is a rear (lingual) elevation of a bracket to show a
preferred way of providing a cement receiving lingual surface
thereon;
FIG. 12 is a part section taken on the line 12--12 of FIG. 11;
and
FIG. 13 is a side elevation similar to FIG. 6 to show the use of a
bracket with a different orientation of the wire relative to the
slot.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the description which follows and in the claims, for convenience
in reference, the parts of the bracket will be referred to using
the conventional directional nomenclature employed by
orthodontists, with the bracket assumed to be mounted on the labial
tooth surface, as is the case in the majority of the procedures
that are undertaken at this time. The brackets of the invention are
however particularly suited for use in lingual procedures, in which
the brackets are instead mounted on the lingual tooth surfaces, so
that they are concealed from view; with this latter technique, the
lingual and labial directions are therefore reversed, and in
addition, owing to the more extreme inclination on the lingual
surfaces of upper incisors in the occlusal-gingival direction, the
"labial" surfaces are designed so that the slot opens in the
occlusal direction and a straight wire technique can be employed.
FIGS. 1 and 2 each include a diagram to show the different
designated directions. Moreover, since it is desired to make the
external surfaces of the bracket as smoothly contoured as possible,
immediately adjoining surface portions will usually merge with one
another without a specific junction edge between them.
Each bracket comprises a body portion 10 which must be mounted on a
respective tooth 12 (FIG. 6); in all of the embodiments illustrated
herein this is done by cementing the lingual face 14 of the body
directly to an acid etched surface of the tooth. Alternatively, as
was the case before cementing systems were developed, and is still
preferred by some orthodontists, the body can be attached to a
tooth embracing band, but this is not illustrated. The lingual
surface 14 of the body is therefore formed, for example as shown in
FIGS. 11 and 12 and described in more detail below, to receive the
cement by which the bracket is attached to the tooth surface. The
surface is also shaped and angled as required in accordance with
the inclination of the tooth and the contour of the tooth surface
to which it is to be attached so as to facilitate the restorative
action of a springy arch wire 16 to which the brackets are
attached. For example, the embodiment illustrated by FIG. 2 has the
lingual surface 14 concave curved toward the lingual direction in
one plane and also inclined at angle .alpha., which in this
embodiment is about 12.degree.; in practice this angle will vary
from 0.degree. to 24.degree.. In the embodiment illustrated by FIG.
3 the surface 14 is concave curved in two directions at right
angles to one another. The shaping and angles that are required for
a complete set of brackets is well known to those skilled in this
particular art and need not be described in further detail
herein.
The body 10 is provided with a substantial recess 18 extending
lingually and gingivally inwards respectively from its labial and
occlusal surfaces so as to leave two spaced occlusal shoulders 20
(mesial side) and 22 (distal side) between which a latch member 24
is mounted for pivoting movement by two spaced coaxial pivot pins
26 between an open position illustrated for example by FIG. 3 and a
closed position illustrated by FIG. 2. The body is also provided to
the gingival side of the occlusal shoulders with a mesio-distal
extending slot 28 which opens to the labial side for insertion of
the arch wire therein. The shape of this slot 28 is best
characterized as rectangular with rounded corners, as is best seen
in FIG. 2. The recess 18 is continued beneath the slot 28 to form
two gingival shoulders 30 and 32 in the respective portion of the
body.
The body is further provided at the lingual side of the slot 28
with a load spring receiving recess 34 that extends gingivally
beyond the slot 28, and also extends lingually deeper into the body
than the arch wire slot so as to be able to receive and retain a
thin curved rectangular load spring 36 which is formed to be convex
in its longer dimension toward the labial opening of the arch wire
slot, and so that a substantial portion of its body between its
ends protrudes into the slot 28, the forward extent of this
protrusion being determined by the engagement of its labial edges
with the labial faces of the recess 34. The protrusion is also such
that with arch wires of the cross-sections and dimensions that are
usually employed, as illustrated by FIGS. 7(a) through 7(f), the
latch member cannot be moved into and latched in its closed
position without at least some contact of the arch wire with the
spring, so that the spring urges the wire against the lingual face
of the closed latch member. If the wire is not fully aligned within
the slot then the spring is even more compressed with the latch
closed, and the restoring spring force on the wire is
correspondingly increased, the spring endeavouring to return to its
position of least strain and applying a corresponding force to the
wire, as will also be described below.
The latch member 24 in this embodiment can be described as of
"comma" cross-section in the occlusal-gingival plane, with the body
24a of the comma receiving the pivot pins 26 perpendicular to that
plane to permit the required pivoting movement, and with the "tail"
24b of the comma constituting the part that closes the labial mouth
of the arch wire slot. The body 24a is provided in the portion of
its face facing the bracket body with a mesio-distal extending
detent 38 providing a gingival-facing ledge surface 40 engagable in
the closed, latched position of FIG. 2 with a latch or detent
spring 42 retained in a corresponding recess 44 in the bracket
body. The latch spring 42 is of the same general configuration as
the load spring 36, namely thin, rectangular and curved in its
longer dimension to be convex toward the latch member. The
curvature to which the spring 42 is normally set is such that in
the closed position of the latch member its protruding occlusal
edge engages beneath the ledge surface 42 and thereby prevents
rotation of the latch member to the open position. The latch is
released by pressing the spring in the lingual direction to flatten
it into the recess 44 until the occlusal edge is freed from the
detent 38; this is accomplished by use of a prod tool 46 (FIG. 2)
having a rounded cylindrical end 48 which is pushed through a
cylindrical bore 50 in the latch member, passing through it from
the labial face to the part of the lingual face opposite the
spring, until it engages the centre of the spring labial face. Two
separate pivot pins 26 are employed to permit the passage of the
tool at the required location.
The occlusal and labial faces of the latch member are smoothly
convexly rounded in their respective directions, as are the
shoulders 20, 22, 30 and 32, so as to avoid sharp edges as much as
possible. The lingual surface of the latch tail 24b is overall
generally concave in transverse cross-section (FIGS. 2 and 3), but
with the part thereof toward the occlusal generally flat and, with
the latch member in the closed position, as parallel as possible to
the lingual face of the arch wire slot. The remaining part toward
the gingival provides almost all of the concavity of this surface,
and in this embodiment it is inclined at about 45.degree. to the
occlusal part, the lingual-labial spacing between it and the slot
lingual face decreasing progressively toward the gingival. The
extreme end 24c of the tail enters between the shoulders 30 and 32
and has its face generally parallel to the adjacent face of the
bracket body. It will be seen that with this shape of the latch
member the effective cross-section of the arch wire slot with the
latch closed corresponds most closely with that of the arch wires
illustrated in FIGS. 7(a) and 7(f). The latch can be closed by
rotation by hand against the force of the load spring 36 until the
tooth spring 42 snaps beneath the detent 38. If desired for
convenience this movement can be effected by use of the tool 46
engaged in the bore 50, but this is not usually required for
leverage purposes since the forces involved are so small.
It is found with my new bracket that it is possible to make it
considerably smaller even than my own prior bracket. Thus,
typically one of my prior brackets measures 3.38 mm (0.133 in.) in
the occlusal-gingival direction; 3 mm (0.140 in.) in the
mesio-distal direction, and about 1.90 to 0.22 mm (0.075 to 0.093
in.) in the lingual-labial direction, the lastmentioned dimension
varying in dependence upon the tooth to which it is to be applied
and consequently the contour, etc. of the lingual face. A bracket
of the present invention can be made with an occlusal-gingival
dimension, which is the most important for consideration of bracket
size in order to reduce tongue irritation, of about 1.93 mm (0.076
in.) and a mesiodistal dimension of 2.59 mm (0.102 in.). The
lingual-labial dimension will also vary in the range 1.47 to 1.93
mm (0.058 to 0.076 in.), depending upon the tooth involved. As
described above built-in torque can be achieved by varying the
angle .alpha. of the lingual surface, avoiding the need with my
prior bracket to angle the slot for this purpose. This has the
effect that the sliding friction of the wire in the different
brackets will remain more constant from bracket to bracket. The
material employed will be any of the usual hard, tough, corrosion
resistant alloys used for orthodontic brackets in the hostil
environment of the human mouth.
In this embodiment the load spring is 1.37 mm (0.054 in.) in length
(mesio-distal); 0.91 mm (0.036 in.) in height (occlusal-gingival)
and is 0.063 mm (0.0025 in.) thick (lingual-labial) and
unconstrained prior to assembly is formed to a radius of 0.76 mm
(0.030 in.). Its radius within the pocket will be of the order of
1.27 mm (0.050 in.). The modulus of the material is such that a
force of about 2-10 ozs will flatten the spring against the
supporting back surface. The latch spring is 1.37 mm (0.054 in.) in
length; 0.48 mm (0.019 in.) in height, and of the same thickness,
the same material and formed to the same radius. It will be seen
that both of the springs are completely concealed and shielded,
with no possibility that they can be constrained beyond their
elastic limit in operation, since this involves movement lingually
into contact with a solid wall that will prevent excessive motion.
There is the possibility of overstressing during assembly, as the
springs are bowed to place them in their respective recesses, but
only because of gross carelessness by a human operator or
mechanical malfunction by an automatic assembler.
In some embodiments the two pivot pins 26 may protrude respectively
mesially and distally beyond the bracket body, as indicated in
broken lines in FIG. 1, to provide anchors for elastics when these
are required. FIG. 6 illustrates the application of brackets of the
invention to lingual procedures, in which the brackets are fastened
to the lingual tooth surfaces. The tooth illustrated is one of the
central incisors and the relative sizes of the tooth and the
bracket will be seen; the profile of the lingual surface of such a
tooth is commonly so extreme that, as illustrated, the bracket
surface that is the labial in the more usual labial procedure is in
this application facing occlusally.
FIGS. 7(a) through 7(f) show the cross-sections of various wires
that may be used with the brackets of the invention. FIGS. 7(c) and
7(e) show respectively the square and circular cross-sections that
are commonly employed, while FIGS. 7(a), 7(b), 7(d) and 7(f) show
wires that are configured specially to cooperate with the concave
lingual surface of the latch tail by having the junction between
the labial and gingival faces smoothly convexly curved, the
cross-sections 7(b) and 7(f) being additionally symetrically
rounded at the occlusal-labial junction. The symmetrical wires of
FIGS. 7(b) and 7(f) permit the brackets, when used in a labial
technique, to be inverted so that excessive bulk can be avoided in
providing the necessary built-in torque. In this embodiment the
arch wire slot has an effective occlusal-gingival dimension of 0.56
mm (0.022 in.) and a lingual-labial dimension adjacent the occlusal
slot face with the load spring unstressed of 0.46 mm (0.018 in.).
This will just accommodate the round wire of FIG. 7(e), which is of
0.46 mm (0.018 in.) diameter and the wires of FIGS. 7(a) and 7(f)
of corresponding dimensions. The "square" wire of FIG. 7(c) will
cause stressing of the load spring because of the engagement of its
labial-gingival junction with the latch member, while the wires of
FIGS. 7(b) and 7(d) will also cause stressing because of their
increased labial-lingual dimension to 0.52 mm (0.020 in.), or even
to as much as 0.56 mm (0.022 in.), which will compress the spring
and increase the friction between the wire and the bracket.
Reference is now made specifically to FIGS. 5, 8, 9 and 10 to
illustrate some of the actions that are possible with the brackets
of the invention. From FIG. 5 it will be seen that the lingual
walls 46 of the arch wire slot 28 between the pairs of shoulders 20
and 30, 22 and 32 are not flat, but are shaped on a radius in a
plane containing the mesial, distal, occlusal and gingival
directions to progressively protrude into the slot toward the
central recess 18; the surfaces therefore conform to the most usual
shape of the portion of the arch wire passing through the bracket,
in that most of the wire is curved to conform to the arch of the
teeth and only the portion associated with the rear molars is
relatively straight.
It is essential in orthodontic practice for the brackets to be able
to slide along the wire to permit the corresponding tooth
displacement, and for this to take place there must be sufficient
clearance between the wall of the slot and the surfaces of the
wires which are used. It is also important that this displacement
take place without lagging of the root portion, which results in
tilting of the tooth in its direction of movement. The manner in
which brackets of the invention operate to prevent such tilting is
illustrated by FIGS. 8(a), 8(b), 9(a) and 9(b). Thus, FIGS. 8(a)
and 8(b) show the situation when the bracket is perpendicular to
the wire, whereupon the wire is in the labial-occlusal corner of
the arch wire slot and the load spring is in its position of least
stress. If the crown of the tooth moves in advance of or behind the
root then the bracket tilts on the wire, as illustrated by FIGS.
9(a) and 9(b), whereupon the load spring is compressed; the attempt
by the spring to return to the position of least stress applies the
necessary corrective rotation to the bracket and hence to the
tooth. It will also be noted that the bracket must rotate about the
occlusal-gingival axis because of the engagement of the wire with
the inclined portion of the latch lingual surface, which will also
counter the natural tendency of the opposite portion of the tooth
to lag in its original position. The bracket in combination with a
round wire is therefore able to control tilting in the
occlusal-gingival plane, as well as rotation in the labial-lingual
plane, but not tipping in the occlusal-gingival plane (i.e. about
the wire longitudinal axis). Control in all three directions,
including the last-mentioned occlusal-gingival plane, can be
achieved by use of one of the wires of non-circular cross-section
as illustrated by FIGS. 10(a) through 10(c). FIG. 10(a) shows the
neutral position with the bracket and tooth "untipped", while FIG.
10(b) shows that when the bracket is tipped lingually the load
spring is stressed and the restoring force (indicated by the arrow)
acts labially, and FIG. 10(c) shows that a lingually-acting
restoring force is provided when the tooth is tipped labially.
FIG. 6 also shows that the shape of the brackets of the invention
is such that they can be surrounded at their junction with the
tooth with an excess of the cement 48 to provide a smooth contoured
body that is less irritating to the tongue. A preferred
configuration for the tooth-engaging surface is illustrated by
FIGS. 11 and 12, namely wherein two sets or pluralities of parallel
grooves 50 and 52 at right angels to one another are formed in the
face to result in a multiplicity of square pillars 54 that engage
the tooth surface. The cement can enter readily into the grooves
and the surplus exit at their ends as the bracket is pressed
against the tooth to provide the cement surround illustrated by
FIG. 6. Such a structure can be produced directly in the bracket
body, e.g. by casting or powder metallurgy, and avoids the need for
a secondary operation to attach a foil mesh or coated foil to act
as a bonding base.
FIG. 13 shows a mesial view of a bracket mounted on the lingual
surface of a second bicuspid tooth employing a wire of the
cross-section shown in FIG. 7(f). At this tooth location, if a
"straight" wire technique is to be employed, the half round side of
the wire is directed toward the occlusal, and the bracket will
accept lingual entry into the slot, which is the only practical way
for the bicuspids and molars, without significant loss of attitude
control.
* * * * *